The present invention relates to a transport refrigeration unit and a method of operating a transport refrigeration unit.
Trucks and tractor-trailer combinations frequently transport cargo that must be maintained at a predetermined temperature (i.e., a set point temperature) or within a predetermined temperature range during transportation. Vehicles that transport temperature sensitive cargo typically have one or more cargo spaces that are maintained within the temperature range by a transport refrigeration unit having an electronic controller, a compressor, a condenser, a flow control valve, an expansion valve, and an evaporator coil. Operation of the transport refrigeration unit is generally controlled and monitored by the electronic controller.
Typically, transport refrigeration units operate in cooling and heating modes, depending, at least in part, upon the temperature of the cargo space and the ambient temperature outside the air-conditioned cargo space. When the temperature of the cargo space is above the set point temperature, the transport refrigeration unit operates in the cooling mode to pull down the temperature in the cargo space. During operation in the cooling mode, refrigerant is directed along a refrigerant circuit, which extends between the compressor, the flow control valve, the condenser, the expansion valve, and the evaporator coil. The cargo space air is then exposed to the relatively cool evaporator coil.
When the temperature of the cargo space is below the set point temperature, the transport refrigeration unit operates in the heating mode. During operation in the heating mode, relatively warm refrigerant is directed through a heating circuit, which extends from the compressor, the flow control valve, and the evaporator coil. The cargo space air is then exposed to the relatively warm evaporator coil.